1. Field of the Invention
The invention relates to a switched-mode power supply circuit comprising a transformer having a primary winding which is arranged in series with a first controllable switch, the series arrangement formed being coupled between the terminals of a d.c. input voltage, the transformer having a first secondary winding to which a rectifier is coupled for making a first d.c. output voltage available and a second secondary winding to which a second controllable switch is coupled for making a second d.c. output voltage available, the circuit further comprising first control means for applying a periodical control signal to the first switch for rendering said switch alternately conducting and non-conducting in dependence upon the first output voltage, as well as second control means for rendering the second switch alternately conducting and non-conducting, the rectifier being conducting when the first switch is blocked and the interval of conductance of the second switch being located in the interval of conductance of the first switch.
A power supply circuit of this type is known from German Patent Application 2,608,167. In this known circuit the first output voltage is maintained substantially constant in spite of possible variations of the input voltage and/or of a load connected to the first output voltage because the intervals of conductance of the first controllable switch are controlled as a function of the first output voltage, and the second output voltage is maintained substantially constant because the intervals of conductance of the second controllable switch are controlled as a function of the second output voltage.